Magnetic disk drive equipment for computers or the like are adapted to drive a magnetic disk of the hard type having a magnetic layer on a rigid substrate relative to a flying magnetic head.
Heretofore, magnetic disks of the coating type have been used in such magnetic disk drives. To meet a demand for increasing the capacity of magnetic disks, magnetic disks of the thin film type having a magnetic thin film, also known as a continuous thin film, which is formed by vapor phase deposition techniques such as sputtering now find increasing use because they have excellent magnetic properties and increased recording density.
The thin film type magnetic disks most often use modified substrates including aluminum alloy substrates having an Ni-P undercoat layer plated thereon or a hard oxide layer formed by anodization. A Cr under layer, a metallic magnetic layer such as a Co-Ni layer, and a protective lubricant layer of carbon or the like are consecutively deposited on the substrate by sputtering.
However, a reliability problem arises because the metallic magnetic layer such as Co-Ni is liable to corrosion and less hard. On the contrary, Japanese Patent Application Kokai Nos. 43819/1987 and 175219/1988 disclose a magnetic thin film based on iron oxide which is chemically stable, resistant against corrosion, and hard enough.
The flying magnetic head has a slider for generating flying forces. The flying magnetic head is generally classified into the composite type in which a core is integrated with the slider and the monolithic type in which a core also serves as the slider.
In addition, great attention is paid to flying thin film magnetic heads for potential maximum density recording. The flying thin film magnetic heads have magnetic pole, gap, coil and other necessary layers formed on a base by vapor phase deposition and other techniques. In these flying thin film heads, the base plays the role of a slider.
A magnetic disk equipment drives a magnetic disk relative to a flying magnetic head in a contact start and stop (CSS) manner so that an impact is applied to the magnetic layer of the disk upon start-up and shut-down because the floating surface of the magnetic head (or the surface of the slider facing the magnetic disk) rests on the magnetic disk before and after the operation.
This tendency is aggravated particularly when a flying thin film magnetic head is used. The magnetic layer undergoes more impact upon CSS because the spacing or flying height between the magnetic disk and the magnetic head is minimized for high density recording.
A magnetic disk having an iron oxide base magnetic thin film as disclosed in Japanese Patent Application Kokai Nos. 43819/1987 and 175219/1988 uses a glass substrate having a mirror finished surface so that the magnetic layer has a surface roughness (Rmax) as low as up to 100 .ANG..
The magnetic disk of this type allows the flying height to be set minimal although the magnetic layer would be more severely damaged if undesired accidental contact occurred between the disk and the head upon CSS or during operation.
Japanese Patent Application Kokai Nos. 43819/1987 and 175219/1988, however, do not refer to the durability of the magnetic layer. No effective proposal for increasing the durability of an iron oxide base magnetic layer of the continuous thin film type is available.
Under these circumstances, the inventors have proposed in U.S. Ser. No. 514,401 filed Apr. 26, 1990 that a magnetic layer predominantly composed of .gamma.Fe.sub.2 O.sub.3 becomes more durable when the layer has controlled peak area ratios in an X-ray diffraction chart thereof or when .alpha.-Fe.sub.2 O.sub.3 is contained in the layer.
In magnetic disks having a magnetic thin film predominantly composed of iron oxide, the magnetic layer has minimal surface roughness as previously described. Unless an appropriate protective layer is chosen, the friction between a magnetic disk and a magnetic head is increased so that the magnetic head would stickily slip or cling to the disk during CSS or the like.